The use of thermoplastics such as polyamides as matrix resins for use in composite or laminate fabrication has one major drawback, they must be processed at and have a heat distortion temperature (HDT) of at least 50.degree. C. above the temperature at which they are to be used so that their modulus or stiffness properties will be acceptable. This problem becomes compounded when an organic fiber is to be used as the reinforcing agent with such a polymer because the fiber also has a characteristic temperature at which it begins to irreversibly lose its stiffness properties. This is generally due to a relaxation phenomenon occurring in a highly oriented fiber.
The case in point is where the fiber to be utilized (of the aromatic polyamide class) in a structural composite application has a relaxation that occurs slightly below 300.degree. C. In order to fabricate a structural laminate with this fiber reinforcement a temperature of 280.degree. C. should not be exceeded in order to assure maximum fiber modulus. This thermal restriction must now in turn be imposed on the resin or polymer meaning it should be processable at a temperature lower than 280.degree. C.
Attempts to develop a polymer which would be thermally and chemically compatible with the fiber led to the development of an aromatic secondary polyamide of the following recurring structure: ##STR1## This polymer had the necessary property of a low HDT (154.degree. C.), but the problem still existed of not being able to utilize the full thermal potential of the fiber (300.degree. C.) because the polymer would soften at the lower temperature. The heating of this polymer to temperatures approaching the relaxation temperature of the fiber had no effect on the polymer's HDT.
There is thus a definite need in the art for an aromatic or aliphatic polyamide resin that can be cured in the region of 300.degree. C. and have a HDT no more than 50.degree.-70.degree. C. below this temperature.
Accordingly, an object of the present invention is to develop a polyamide which can be processed at or below 300.degree. C. due to a low HDT and then subsequently attain a higher HDT due to a chemical conversion which occurs during the thermal treatment.
Another object of the present invention is a novel polyamide which can be utilized for fabricating structural composites.
Another object of the present invention is a novel polyamide or series of polyamides which can be utilized as thermoset-thermoplastics due to a latent chemical conversion.
Another object of the present invention is a novel process of preparing a thermoset-thermoplastic molding material.
Another object of the present invention is a novel process for fabricating a structural composite which is solvent resistant.
Another object of the present invention is a novel process for fabricating structure composites.
Another object of the present invention is a novel polymer which is soluble before thermal processing, but solvent resistant after this processing.